1. Field of the Invention
The invention relates to a gain-controlled amplifier arrangement comprising a cascade arrangement of first and second gain-controlled amplifier stages, an AM-detection circuit and an integrating arrangement for generating a control voltage for the two stages, also comprising a threshold arrangement for generating first and second threshold voltages for delaying with an increasing input level the start of the control of the first stage relative to that of the second stage.
2. Description of the Prior Art
Such a gain-controlled amplifier arrangement is disclosed in U.S. Pat. No. 3,665,317.
The prior art amplifier arrangement produces an output signal whose amplitude is stabilized at a desired value, to a certain extent independent of the input signal level. To that end use is made of what is commonly referred to as delayed gain control. Therewith a maximum gain is effected for low input signal levels in the two stages and at an increasing input signal level first the gain of the last stage--i.e. the second stage--in the transmission path is reduced from a certain threshold level denoted the second threshold value hereinafter, followed by a gain reduction of the preceding,--i.e. first--stage when the input signal level exceeds a higher, so-called first threshold value. These threshold values are adjusted by means of the said threshold voltages such that the input signal level is adequately high upon reaching the respective threshold values to prevent a deterioration of the noise factor because of a gain reduction of the relevant stage from noticeably affecting the signal-to-noise ratio.
In the known amplifier arrangement deviations in the threshold voltages, caused, for example, by tolerance spread, temperature fluctuation or ageing not only cause an impermissible deviation of the output level but also an unwanted significant variation of the control rate and of the noise and distortion of the output signal in the control range. So it may, for example, happen that in a part of the overall control range both stages are simultaneously in a control state and together determine the control rate. It may also happen that the control range of the second stage in which an acceptable signal processing occurs is utilized over a too small part and the gain of the first stage is prematurely reduced, causing the noise contribution of the first stage to become undesirably great. It may further happen, that said control range of the second stage to be exceeded and consequently an impermissible signal distortion to be produced.